Light-emitting layer, organic light emitting diode device and display apparatus

ABSTRACT

The present disclosure provides a light-emitting layer, an organic light emitting diode (OLED) device, and a display apparatus. The light-emitting layer has a host material containing a first photocrosslinker group. A guest material containing a second photocrosslinker group is prepared. The host material and the guest material are mixed in a solvent to form a mixture. The mixture is coated, annealed, and LV-irradiated on a substrate to form the light-emitting layer. As such, the disclosed light-emitting layer is prepared by the polymerization after being on the substrate. The light-emitting layer has a mesh structure. The mesh structure improves energy transfer between the host material and guest material and increases the lifespan of the resultant OLED device and OLED display apparatus.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.15/758,089, filed on Mar. 7, 2018, which claims priority of ChinesePatent Application No. 201410828765.4, filed on Dec. 26, 2014, theentire content of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure generally relates to the field of displaytechnologies and, more particularly, relates to light-emitting layersand preparation method thereof, and corresponding organic light emittingdiode (OLED) devices and display apparatus.

BACKGROUND

Currently, monitors for display include cathode ray tube, liquid crystaldisplay (LCD), vacuum fluorescent device, plasma display, organic lightemitting diode (OLED), field emission display, and electroluminescentdisplay.

Compared with LCD, OLED as a flat panel display is thin and lightweight,and may have wide viewing angle, active light emitting, adjustable lightcolor, low cost, fast response, low energy consumption, low drivingvoltage, wide operating temperature range, simple preparation process,high efficiency, and/or flexible display. The OLED technology has drawngreat attention in industrial and scientific communities.

An OLED device often includes a functional layer and a light-emittinglayer, which determine wavelength of the emitted light and also affectlight-emitting efficiency and life span of the OLED device. Because aphosphorescent OLED device is able to use both the singlet and tripletexcitons to enhance the external quantum efficiency of the OLED device,the phosphorescent OLED has been widely adopted in OLED devices.

The light-emitting layer of the phosphorescent OLED device includes ahost material and a guest material. In existing technologies, the guestmaterial is often a rare earth metal complex, and the host material isoften an ordinary organic compound. Such host material and the guestmaterial are prone to a phase separation. Lifespan of the OLED device istherefore shortened. However, the emerging of a polymer OLED devicesolves the above problems.

Methods for preparing high efficiency polymer OLED devices may focus onmolecular structures and preparation processes. However, crosslinkingwith high degree may occur between the host material and guest material,and may reduce solubility of the materials. This may adversely affectformation of the light-emitting layer in the OLED devices.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure provides a method for forming alight-emitting layer. In the method, a host material containing a firstphotocrosslinker group is prepared. A guest material containing a secondphotocrosslinker group is prepared. The host material and the guestmaterial are mixed in a solvent to form a mixture. The mixture iscoated, annealed, and UV-irradiated on a substrate to form thelight-emitting layer.

Optionally, the host material contains a plurality of firstphotocrosslinker groups.

Optionally, the first photocrosslinker group and the secondphotocrossinker group are independently selected from methacrylamide,methacrloyl chloride, N-alkyl maleimide, β-dicarbonyl compounds, and acombination thereof.

Optionally, the host material is at least one of:

where x, n, and mare respectively an integer greater than 1, and thehost material has a molecular weight between approximately 3000 and100000.

Optionally, the guest material is prepared from a polycondensation of arare earth metal complex as a hydroxyl group donor and the secondphotocrosslinker group. The rare earth metal is at least one oflanthanum, cerium, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium, scandium, and yttrium.

Optionally, the guest material is at least one of:

Optionally, the substrate is suitable for an organic light emittingdiode (OLED) device. Optionally, after coating the mixture on thesubstrate and before the UV-irradiating, the coated mixture is annealed.

Optionally, a molar ratio of the host material to the guest material isapproximately 100:2. Optionally, the UV-irradiating is performed forapproximately 30 minutes.

Another aspect of the present disclosure provides a light-emitting layerprepared by the disclosed methods. The prepared light-emitting layer hasa mesh structure.

Another aspect of the present disclosure provides an organic lightemitting diode (OLED) device including the disclosed light-emittinglayer. Another aspect of the present disclosure provides a displayapparatus including the disclosed organic light emitting diode device.

Other aspects of the present disclosure can be understood by thoseskilled in the art in light of the description, the claims, and thedrawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present disclosure.

FIG. 1 illustrates an synthetic pathway for an exemplary host materialaccording to various disclosed embodiments;

FIG. 2 illustrates an synthetic pathway for an exemplary guest materialaccording to various disclosed embodiments;

FIG. 3 illustrates an synthetic pathway for another exemplary hostmaterial according to various disclosed embodiments;

FIG. 4 illustrates an synthetic pathway for another exemplary guestmaterial according to various disclosed embodiments; and

FIG. 5 illustrates a schematic structure diagram of an exemplary organiclight emitting diode device according to various disclosed embodiments;and

FIG. 6 illustrates a block diagram of an exemplary display apparatusaccording to the disclosed embodiments.

DETAILED DESCRIPTION

In order for those skilled in the art to better understand the technicalsolutions of the present invention, the followings together withaccompanying drawings describe in detail the present invention withspecific embodiments.

The present disclosure provides a light-emitting layer. Thelight-emitting layer is synthesized from a host material containing aplurality of first photoactive groups such as first photocrosslinkergroups, and a guest material containing a second photoactive group suchas a second photocrosslinker group. In one embodiment, the host materialis a polymer host material.

FIG. 1 illustrates a synthetic pathway for an exemplary host materialaccording to various disclosed embodiments. Following the syntheticpathway shown in FIG. 1, a host material A1 is prepared.

For example, a nitrogen inlet, a stirrer, a heater, a condenser and athermometer are configured on a flask, such as a 4-neck flask. At thebeginning toluene is used as a solvent and is added in the flask, andthe nitrogen is introduced into the toluene solvent.

Next, a host material precursor A01 of the host material A1, containinghydroxyl repeating units, is added in the flask. Methacryloyl chlorideis used as a photocrosslinker group and is added into the host materialprecursor A01 in the flask in a molar amount of about 2 times of thehost material precursor A01.

In a dark environment, under the protection of nitrogen, at 60 degreesCelsius, after 3 hours of hydroxyl polycondensation (or condensationpolymerization) reaction with the host material precursor A01, thephotocrosslinker group is covalently attached to the host materialprecursor A01.

Upon completion of the hydroxyl polycondensation reaction, toluene isadded. By stirring and washing, a polymer is precipitated. Aftercentrifugal filtration, the host material A1 containing at least onerepeating unit that contains at least one photocrosslinker group isobtained.

As shown in FIG. 1, in the structural formula of the host material A1, nand m are respectively an integer greater than 1. In one embodiment, themolecular weight of the host material A1 is between approximately 3000and 100000, for example, between approximately 3000 and 5000, such asapproximately 3000.

An infrared (IR) spectrum analysis is performed on the host material A1.The IR spectrum indicates an absorption peak at wavenumber 1722 cm⁻¹,which is known as the absorption peak of the ester carbonyl group. Thatis, the produced host material A1 contains ester carbonyl group.

Following the similar procedure illustrated in FIG. 1, a guest materialB1 is prepared in the synthetic pathway illustrated in FIG. 2.

A nitrogen inlet, a stirrer, a heater, a condenser, and a thermometerare configured on a flask such as a 4-neck flask. At the beginning,toluene is used as a solvent and is added in the flask, and nitrogen isintroduced into the toluene solvent.

Next, a guest material precursor B01 of the guest material B1,containing a hydroxyl group, is added in the flask. Methacryloylchloride is used as a photocrosslinker group and is added into the guestmaterial precursor B01 in the flask in a molar amount of about 2 timesof the guest material precursor B01.

In dark environment, under the protection of nitrogen, at 60 degreesCelsius, after 3 hours of hydroxyl polycondensation with the guestmaterial precursor B01, the photocrosslinker group is covalentlyattached to the guest material precursor B01 of the guest material.

Upon completion of the hydroxyl polycondensation reaction, toluene isadded. By stirring and washing, a compound is precipitated. Aftercentrifugal filtration, the guest material B1 containing thephotocrosslinker group is obtained.

After the preparation of the host material A1 and the guest material B1,a light-emitting layer is prepared as follows.

At the beginning, the host material A1 and the guest material B1 aremixed and dissolved in a toluene solvent to form a mixture. A molarratio of the host material A1 to the guest material B1 is about 100:2.

The mixture of the host material A1 and the guest material B1 is thenspin-coated on a substrate; annealed at about 100 degrees Celsius forabout 20 minutes, and irradiated under UV light for about 30 minutes toallow a complete polymerization of the host material A1 and the guestmaterial B1 to produce AB1, which can be used as a light-emitting layer.

FIG. 3 illustrates a synthetic pathway for another exemplary hostmaterial according to various disclosed embodiments. Following thesynthetic pathway shown in FIG. 3, a host material A2 is synthesized.

At the beginning, a nitrogen inlet, a stirrer, a heater, a condenser,and a thermometer are configured on a flask such as a 4-neck flask. Thetoluene is used as a solvent and is added in the flask, and nitrogen isintroduced into the toluene solvent.

Next, a host material precursor A02 of the host material A2, containinghydroxyl repeating units, is added in flask. Methacryloyl chloride isused as a photocrosslinker group and is added into the host materialprecursor A02 in the flask in a molar amount of about 2 times of thehost material precursor A01.

In a dark environment, under the protection of nitrogen, at about 60degrees Celsius, after about 3 hours of hydroxyl polycondensationreaction with the host material precursor A02, the photocrosslinkergroup is covalently attached to the host material precursor A02.

Upon completion of the hydroxyl polycondensation reaction, toluene isadded. By stirring and washing, a polymer is precipitated. Aftercentrifugal filtration, the host material A2 containing at least onerepeating unit of the photocrosslinker group is obtained.

As shown in FIG. 3, in the structural formula of the host material A2, nand x are respectively an integer greater than 1. The molecular weightof the host material A2 is between about 3000 and about 100000, such asabout 100000.

An infrared (IR) spectrum analysis is performed on the host material A2.The IR spectrum indicates an absorption peak at wavenumber 1722 cm⁻¹,which is known as the absorption peak of ester carbonyl group. That is,the produced host material A2 contains ester carbonyl group.

Similar procedure is used to prepare a guest material B2. Following thespecific synthetic pathway shown in FIG. 4, the guest material B2 issynthesized.

At the beginning, a nitrogen inlet, a stirrer, a heater, a condenser,and a thermometer are configured on a flask such as a 4-neck flask.Toluene is used as a solvent and is added in flask, and nitrogen isintroduced into the toluene solvent.

Next, a guest material precursor B02 of the guest material B2,containing a hydroxyl group, is added in the flask. Methacryloylchloride is used as a photocrosslinker group and is added into the guestmaterial precursor B02 in the flask in a molar amount of about 2 timesof the guest material precursor B02.

In dark environment, under the protection of nitrogen, at about 30-60degrees Celsius, after 3 hours of hydroxyl polycondensation with theguest material precursor B02, the photocrosslinker group is covalentlyattached to the guest material precursor B02 of the guest material B2.

Upon completion of the hydroxyl polycondensation reaction, toluene isadded. By stirring and washing, a compound is precipitated. Aftercentrifugal filtration, the guest material B2 containing thephotocrosslinker group is obtained.

After the preparation of the host material A2 and the guest material B2,another exemplary light-emitting layer may be prepared as follows.

At the beginning, the host material A2 and the guest material B2 aremixed and dissolved in a toluene solvent to form a mixture. A molarratio of the host material A2 to the guest material B2 is about 100:2.

The mixture of the host material A2 and the guest material B2 isspin-coated on a substrate, annealed at about 100 degrees Celsius forabout 20 minutes, and UV-irradiated for about 30 minutes to allow thehost material A2 and the guest material B2 to be completely polymerizedto produce AB2, which can be used as an exemplary light-emitting layer.

In various embodiments, the photocrosslinker group may be selected frommethacrylamide, N-alkyl maleimide, β-dicarbonyl compounds, orcombinations thereof. The photocrosslinker group can react with thehydroxyl group contained in the precursors of the host material and/orthe guest material, and thus to be covalently attached to correspondinghost material and/or guest material. The photocrosslinker groupsattached on the host material and/or guest material may undergopolycondensation reaction under ultraviolet (UV) irradiation to producea mesh structure to form the light-emitting layer. Thus, the guestmaterial can be substantially, uniformly distributed in the hostmaterial.

Any suitable methods can be used in the present disclosure to attachphotocrosslinker groups to the host material and/or the guest material,based on the structural characteristics of the photocrosslinker groups,the host material, and the guest material. In addition, any suitablecrosslinking parameters can be used for the photocrosslinker groups inthe present disclosure for the UV crosslinking process of the hostmaterial and guest material.

The present disclosure also provides an organic light emitting diode(OLED) device. As shown in FIG. 5, the OLED device includes a substrate,an anode, a hole-transport layer, a light-emitting layer (EML), anelectron transport layer, and a cathode. More layers may be included,and existing layers may be modified, omitted, or rearranged in the OLEDdevice.

In an exemplary OLED device, the anode on the substrate may include anindium tin oxide (ITO) coated glass substrate. The hole-transport layermay include a poly(3,4-ethylenedioxythiophene):(polystyrene sulfonicacid) (PEDOT:PSS) film. The electron transport layer may include1,3,5,-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI). The cathode mayinclude a two layer structure of CsF/Al. In various embodiments, the CsFlayer may be interchangeable with any suitable fluoride of an alkalimetal or an alkaline earth metal, such as LiF, CaF₂, and BaF₂. In oneembodiment, the OLED device may be ITO/PEDOT:PSS (40 nm)/EML (70nm)/TPBI (30 nm)/CsF(1.5 nm)/Al(120 nm).

The light-emitting layer (EML) may have a mesh structure and may beprepared based on the host material A1 and the guest material B throughthe synthetic pathway illustrated in FIGS. 1-2.

The anode of the OLED device, the ITO coated glass substrate, may beprepared by an ultrasonic cleaning in acetone, detergent, deionizedwater and isopropanol. After cleaning, the substrate is dried in anoven.

The cleaned substrate is then treated with oxygen plasma to improve workfunction of the ITO and to further remove the organic contaminantsremaining on the surface of the substrate to improve the surface contactangle of the substrate. Further, the substrate is spin-coated withPEDOT:PSS film to increase the Fermi energy level of the ITO to bebetween about −5.2 to about −5.3 eV. This greatly reduces the holeinjection barrier from the anode.

After the spin-coated substrate is dried in a vacuum oven at about 80degrees Celsius for about 8 hours, the substrate is moved into anitrogen filled glove box for preparing the light-emitting layer. Thehost material A1 and the guest material B1 are mixed and dissolved in atoluene solvent to form a mixture having a molar ratio of the hostmaterial A1 and the guest material B1 of about 100:2.

After the mixture of the host material A1 and the guest material B forpreparing the light-emitting layer is spin-coated on the substrate,annealed at about 100 degrees Celsius for about 20 minutes, UVirradiated for about 30 minutes, a complete polymerization of the hostmaterial A1 and the guest material B1 can be performed to produce anexemplary light-emitting layer (EMIL).

In one embodiment, under high vacuum environment of less than about3×10⁻⁴ Pa, a film of CsF(1.5 nm)/Al(120 nm) is deposited on thesubstrate as the cathode using thermal evaporation techniques.

As disclosed, the host material A1 and the guest material B1 arespin-coated first and then polymerized. Solubility reduction, occurredin conventional methods during a polymerization before the spin-coating,may be avoided.

Table 1 compares test results of the disclosed OLED devices and aconventional OLED device using a same light source for forming thelight-emitting layer.

TABLE 1 EML Lifespan (Hours) Existing OLED device 1000 Exemplary OLEDdevice (having AB1 as EML) 1300 Exemplary OLED device (having AB2 asEML) 1500

As shown in Table 1, the lifespan of the disclosed OLED devices usingthe produced AB1 and AB2 as light-emitting layers is significantlyimproved, compared with conventional OLED device. In one embodiment, thedisclosed OLED devices may have similar structures and preparationmethods, for example, as illustrated in FIG. 5.

FIG. 6 illustrates an exemplary display apparatus 600 incorporatingcertain disclosed embodiments. The display apparatus 600 may be anyappropriate device or component with certain display functions, such asan OLED panel, an OLED TV, a monitor, a cell phone or smartphone, acomputer, a tablet, or a navigation system, or any products orcomponents with OLED devices disclosed in the above embodiments. Asshown in FIG. 6, the display apparatus 600 includes a controller 602, adriving circuit 604, memory 606, peripherals 608, and a display panel610.

The controller 602 may include any appropriate processor or processors,such as a general-purpose microprocessor, digital signal processor,and/or graphic processor. Further, the controller 602 can includemultiple cores for multi-thread or parallel processing. The memory 606may include any appropriate memory modules, such as read-only memory(ROM), random access memory (RAM), flash memory modules, and erasableand rewritable memory, and other storage media such as CD-ROM, U-disk,and hard disk, etc. The memory 606 may store computer programs forimplementing various processes, when executed by the controller 602.

Peripherals 608 may include any interface devices for providing varioussignal interfaces, such as USB, HDMI, VGA, DVI, etc. Further,peripherals 608 may include any input and output (I/O) devices, such askeyboard, mouse, and/or remote controller devices. Peripherals 608 mayalso include any appropriate communication module for establishingconnections through wired or wireless communication networks.

The driving circuit 604 may include any appropriate driving circuits todrive the display panel 610. The display panel 610 may include anyappropriate OLED devices disclosed in the above embodiments. Duringoperation, the display 610 may be provided with image signals or othersource data signals by the controller 602 and the driving circuit 604for display.

The embodiments disclosed herein are exemplary only and not limiting thescope of this disclosure. Various alternations, modifications, orequivalents to the technical solutions of the disclosed embodiments canbe obvious to those skilled in the art and can be included in thisdisclosure. Without departing from the spirit and scope of thisinvention, such other modifications, equivalents, or improvements to thedisclosed embodiments are intended to be encompassed within the scope ofthe present disclosure.

What is claimed is:
 1. A light-emitting layer, comprising: a mixture,including a host material containing a first photocrosslinker group anda guest material containing a second photocrosslinker group in asolvent, on a substrate, wherein: the light-emitting layer is aUV-irradiated mixture on the substrate, and the light-emitting layer hasa mesh structure, wherein the host material is at least one of:

wherein x, n, and m are respectively an integer greater than 1, and thehost material has a molecular weight between approximately 3000 and100000.
 2. An organic light emitting diode device comprising thelight-emitting layer according to claim
 1. 3. A display apparatuscomprising the organic light emitting diode device according to claim 2.4. The light-emitting layer according to claim 1, wherein: the hostmaterial contains a plurality of first photocrosslinker groups.
 5. Thelight-emitting layer according to claim 1, wherein: the firstphotocrosslinker group and the second photocrosslinker group areindependently selected from methacrylamide, methacrloyl chloride,N-alkyl maleimide, β-dicarbonyl compounds, and a combination thereof. 6.The light-emitting layer according to claim 1, wherein: the guestmaterial is prepared from a polycondensation of a rare earth metalcomplex as a hydroxyl group donor and the second photocrosslinker group.7. The light-emitting layer according to claim 1, wherein the guestmaterial is at least one of:


8. The light-emitting layer according to claim 1, wherein: a molar ratioof the polymer host material to the guest material is approximately100:2.